freeCodeCamp/curriculum/challenges/english/03-front-end-development-libraries/react/use-a-ternary-expression-for-conditional-rendering.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5a24c314108439a4d4036187	Use a Ternary Expression for Conditional Rendering	6	301414	use-a-ternary-expression-for-conditional-rendering

--description--

Before moving on to dynamic rendering techniques, there's one last way to use built-in JavaScript conditionals to render what you want: the ternary operator. The ternary operator is often utilized as a shortcut for if/else statements in JavaScript. They're not quite as robust as traditional if/else statements, but they are very popular among React developers. One reason for this is because of how JSX is compiled, if/else statements can't be inserted directly into JSX code. You might have noticed this a couple challenges ago — when an if/else statement was required, it was always outside the return statement. Ternary expressions can be an excellent alternative if you want to implement conditional logic within your JSX. Recall that a ternary operator has three parts, but you can combine several ternary expressions together. Here's the basic syntax:

condition ? expressionIfTrue : expressionIfFalse;

--instructions--

The code editor has three constants defined within the CheckUserAge component's render() method. They are called buttonOne, buttonTwo, and buttonThree. Each of these is assigned a simple JSX expression representing a button element. First, initialize the state of CheckUserAge with input and userAge both set to values of an empty string.

Once the component is rendering information to the page, users should have a way to interact with it. Within the component's return statement, set up a ternary expression that implements the following logic: when the page first loads, render the submit button, buttonOne, to the page. Then, when a user enters their age and clicks the button, render a different button based on the age. If a user enters a number less than 18, render buttonThree. If a user enters a number greater than or equal to 18, render buttonTwo.

--hints--

The CheckUserAge component should render with a single input element and a single button element.

assert(
  Enzyme.mount(React.createElement(CheckUserAge)).find('div').find('input')
    .length === 1 &&
    Enzyme.mount(React.createElement(CheckUserAge)).find('div').find('button')
      .length === 1
);

The CheckUserAge component's state should be initialized with a property of userAge and a property of input, both set to a value of an empty string.

assert(
  Enzyme.mount(React.createElement(CheckUserAge)).state().input === '' &&
    Enzyme.mount(React.createElement(CheckUserAge)).state().userAge === ''
);

When the CheckUserAge component is first rendered to the DOM, the button's inner text should be Submit.

assert(
  Enzyme.mount(React.createElement(CheckUserAge)).find('button').text() ===
    'Submit'
);

When a number of less than 18 is entered into the input element and the button is clicked, the button's inner text should read You Shall Not Pass.

(() => {
  const mockedComponent = Enzyme.mount(React.createElement(CheckUserAge));
  const initialButton = mockedComponent.find('button').text();
  const enter3AndClickButton = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: '3' } });
    mockedComponent.find('button').simulate('click');
    mockedComponent.update();
    return mockedComponent.find('button').text();
  };
  const enter17AndClickButton = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: '17' } });
    mockedComponent.find('button').simulate('click');
    mockedComponent.update();
    return mockedComponent.find('button').text();
  };
  const userAge3 = enter3AndClickButton();
  const userAge17 = enter17AndClickButton();
  assert(
    initialButton === 'Submit' &&
      userAge3 === 'You Shall Not Pass' &&
      userAge17 === 'You Shall Not Pass'
  );
})();

When a number greater than or equal to 18 is entered into the input element and the button is clicked, the button's inner text should read You May Enter.

(() => {
  const mockedComponent = Enzyme.mount(React.createElement(CheckUserAge));
  const initialButton = mockedComponent.find('button').text();
  const enter18AndClickButton = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: '18' } });
    mockedComponent.find('button').simulate('click');
    mockedComponent.update();
    return mockedComponent.find('button').text();
  };
  const enter35AndClickButton = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: '35' } });
    mockedComponent.find('button').simulate('click');
    mockedComponent.update();
    return mockedComponent.find('button').text();
  };
  const userAge18 = enter18AndClickButton();
  const userAge35 = enter35AndClickButton();
  assert(
    initialButton === 'Submit' &&
      userAge18 === 'You May Enter' &&
      userAge35 === 'You May Enter'
  );
})();

Once a number has been submitted, and the value of the input is once again changed, the button should return to reading Submit.

(() => {
  const mockedComponent = Enzyme.mount(React.createElement(CheckUserAge));
  const enter18AndClickButton = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: '18' } });
    mockedComponent.find('button').simulate('click');
    mockedComponent.update();
    return mockedComponent.find('button').text();
  };
  const changeInputDontClickButton = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: '5' } });
    mockedComponent.update();
    return mockedComponent.find('button').text();
  };
  const enter10AndClickButton = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: '10' } });
    mockedComponent.find('button').simulate('click');
    mockedComponent.update();
    return mockedComponent.find('button').text();
  };
  const userAge18 = enter18AndClickButton();
  const changeInput1 = changeInputDontClickButton();
  const userAge10 = enter10AndClickButton();
  const changeInput2 = changeInputDontClickButton();
  assert(
    userAge18 === 'You May Enter' &&
      changeInput1 === 'Submit' &&
      userAge10 === 'You Shall Not Pass' &&
      changeInput2 === 'Submit'
  );
})();

Your code should not contain any if/else statements.

assert(
  new RegExp(/(\s|;)if(\s|\()/).test(
    Enzyme.mount(React.createElement(CheckUserAge)).instance().render.toString()
  ) === false
);

--seed--

--after-user-code--

ReactDOM.render(<CheckUserAge />, document.getElementById('root'));

--seed-contents--

const inputStyle = {
  width: 235,
  margin: 5
};

class CheckUserAge extends React.Component {
  constructor(props) {
    super(props);
    // Change code below this line

    // Change code above this line
    this.submit = this.submit.bind(this);
    this.handleChange = this.handleChange.bind(this);
  }
  handleChange(e) {
    this.setState({
      input: e.target.value,
      userAge: ''
    });
  }
  submit() {
    this.setState(state => ({
      userAge: state.input
    }));
  }
  render() {
    const buttonOne = <button onClick={this.submit}>Submit</button>;
    const buttonTwo = <button>You May Enter</button>;
    const buttonThree = <button>You Shall Not Pass</button>;
    return (
      <div>
        <h3>Enter Your Age to Continue</h3>
        <input
          style={inputStyle}
          type='number'
          value={this.state.input}
          onChange={this.handleChange}
        />
        <br />
        {/* Change code below this line */}

        {/* Change code above this line */}
      </div>
    );
  }
}

--solutions--

const inputStyle = {
  width: 235,
  margin: 5
};

class CheckUserAge extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      userAge: '',
      input: ''
    };
    this.submit = this.submit.bind(this);
    this.handleChange = this.handleChange.bind(this);
  }
  handleChange(e) {
    this.setState({
      input: e.target.value,
      userAge: ''
    });
  }
  submit() {
    this.setState(state => ({
      userAge: state.input
    }));
  }
  render() {
    const buttonOne = <button onClick={this.submit}>Submit</button>;
    const buttonTwo = <button>You May Enter</button>;
    const buttonThree = <button>You Shall Not Pass</button>;
    return (
      <div>
        <h3>Enter Your Age to Continue</h3>
        <input
          style={inputStyle}
          type='number'
          value={this.state.input}
          onChange={this.handleChange}
        />
        <br />
        {this.state.userAge === ''
          ? buttonOne
          : this.state.userAge >= 18
          ? buttonTwo
          : buttonThree}
      </div>
    );
  }
}